This invention relates to a heater for a grain bin or the like in which air is heated by a gas fired burner and then in ducted into a grain bin or other structure for drying or otherwise conditioning grain therein. Conventionally, such grain bin heaters include a housing which may be connected to a grain bin for directing heated air therefrom into the grain bin. A fan forcefully moves air through the housing, past a burner therein, and directs the heated air into the grain bin. Oftentimes the grain bin has a perforated floor raised above a concrete pad with the space between the floor and the concrete pad constituting a plenum chamber. The heater directs heated air under pressure into this plenum chamber where it is substantially uniformly distributed under the entire cross section of the grain bin such that the heated air may pass upwardly through the floor and through the grain supported on the floor so as to dry the grain.
Conventionally, most grain bin dryers are gas fired dryers which burn either liquefied petroleum (e.g., liquid propane) or natural gas. The dryer fan may be either an axially blower located upstream from the heater (as shown in FIGS. 2 and 3) and generally in axial alignment with the heater, or the fan may be a centrifugal fan (not illustrated) coupled to the heater upstream from the heater. Such heaters typically include a gas burner positioned within the central portion of the heater housing so that when the gas fuel is ignited, a flame is generated which heats the air forced by the fan through the heater housing and into the grain bin. It has been long known that by providing such gas fired grain bin heaters with a flame diverter that the flame can be more uniformly distributed within the housing thus resulting in better heating of the air being forced through the heater. Typically, such prior art flame diverters comprise a plurality of spaced slats arranged in a generally conical configuration with the apex of the conical diverter being positioned close to the burner at the center of the heater housing so as to direct the flame outwardly toward the walls of the housing. Typically, these flame diverter slats are provided with a multiplicity of holes therein so as to aid in supplying air to the air/fuel mixture.
In a gas burner, the gas fuel has a certain calorific value typically expressed in BTU/cubic foot of the gas fuel. For example, natural gas may have a calorific value of about 1,000 BTU/cu. ft., and commercially available propane L.P. gas may have a calorific value of about 2,350 BTU/cu. ft. If these gaseous fuels are completely combusted, the products of combustion will include carbon dioxide, water, and nitrogen compounds from the combustion air. Of course, such complete combustion insures the maximum release of heat from the fuel and results in the most efficient operation of the burner. Such complete combustion of the fuel results in the maximum amount of air being heated. Complete combustion of the fuel is usually visually evidenced by the flame burning with a bluish or colorless flame. If combustion is incomplete, as will be the case if there is not sufficient air for complete combustion, carbon monoxide and carbon with also make up part of the combustion products. It is well recognized that the presence of a "yellowish" flame is a sign that incomplete combustion (and thus less efficient combustion) is occurring such that the maximum efficiency of the burner is not being realized.
In many prior art grain dryer heaters such as above-described, it has long been noted that at least certain portions of the flame within the burner has had a generally yellowish appearance which is an indication of incomplete combustion. Typically, such areas of incomplete combustion were immediately downstream from the burner nozzle located at the center of the grain bin heater housing. However, with the known prior art grain burners it has not heretofore been possible to regulate the position of the flame within the heater housing so as to achieve both complete combustion and to divert the flame outwardly toward the walls of the housing so as to result in a more evenly distributed heating of the air. The above-described prior art flame diverters with their spaced slats did effectively direct the flames outwardly from the burner toward the walls of the housing, but such flame diverters (even when their spaced slats were provided with a multiplicity of holes therein) were not effective so as to insure that complete combustion of the gaseous fuel would result even if the burner was regulated to admit more air into the burner for mixing with the fuel prior to the point the fuel was ignited. As above-noted, in conventional prior art grain bin dryers (as shown in FIG. 2), a region of low pressure would develop immediately downstream from the burner nozzle such that when the fuel burned in this area, it would burn with a "yellowish" color flame generally indicative of incomplete combustion.
Thus, there has been a long-standing problem as to how to insure complete combustion for maximum efficiency of the heater and to simultaneously uniformly distribute the heated air with the air forcefully moved through the heater without duly restricting the flow of air through the blower/heater unit.